Conventionally, a battery case housing a plurality of battery cells is provided with a voltage detection circuit board to detect the voltage of each battery cell. For example, Patent Literature 1 shows the structure of a pack battery including a battery core (1) storing a plurality of batteries (2) in a battery case (3), and a circuit board (4) connected to the batteries (2) of the battery core (1) via leads and secured at a fixed position in the battery core (1).